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This indicator comprises several metrics to describe past and future sea-level rise globally and in European seas. Global sea-level rise is reported because it is the second-most important metric of global climate change (after global mean surface temperature), and because it is a proxy of sea-level rise in Europe. Past sea-level trends across Europe are reported in two different ways: first, absolute sea level change based on satellite altimeter measurements that reflect primarily the contribution of global climate change to sea-level rise in Europe; second, relative sea-level change based on tide gauges that also include local land movement, which is more relevant for the development of regional adaptation strategies.
The following components on observed sea-level rise are included:
Change in global mean sea level (time series starting in 1880, in mm), based on a reconstruction from various data sources (since 1880) and on satellite altimeter data (since 1993)
Trend in absolute sea level across Europe (map, in mm/year), based on satellite measurements (since 1992)
Trend in relative sea level across Europe (map, in mm/year), based on selected European tide gauge stations (since 1970)
Furthermore, this indicator presents projections for sea level rise in the 21st century, both globally and for the European seas. The indidator also presents the contributions to past and future global sea level rise from different sources.
Finally, the indicator presents information on observed and projected changes in extreme sea level along European coasts. However, due to insufficient data availability this information cannot be presented by means of figures or maps.

Assessment versions

Published (reviewed and quality assured)

Rationale

Justification for indicator selection

Sea level is an important indicator of climate change because it is associated with significant potential impacts on settlements, infrastructure, people and natural systems. It acts on time scales much longer than those of indicators that are closely related to near-surface temperature change. Even if greenhouse gas concentrations were stabilised immediately, sea level would continue to rise for many centuries.

Changes in global average sea level result from a combination of several physical processes. Thermal expansion of the oceans occurs as a result of warming ocean water. Additional water is added to the ocean from a net melting of glaciers and small ice caps, and from the large Greenland and Antarctic ice sheets. Further contributions may come from changes in the storage of liquid water on land, either in natural reservoirs such as groundwater or man-made reservoirs.

The locally experienced changes in sea level differ from global average changes for various reasons. Firstly, changes in water density are not expected to be spatially uniform, and the spatial pattern also depends on changes in large-scale ocean circulation. Secondly, changes in the gravity field, for instance as water moves from melting land ice to the ocean, also varies across regions. Finally, at any particular location there may be a vertical movement of the land in either direction, for example due to the post-glacial rebound (in northern Europe) or to local groundwater extraction.

Low-lying coastlines with high population densities and small tidal ranges are most vulnerable to sea-level rise, in particular where adaptation is hindered by a lack of economic resources or by other constraints. InEurope, the potential impacts of sea-level rise include flooding, coastal erosion, and the loss of flat coastal regions. Rising sea levels can also cause salt-water intrusion into low-lying aquifers, thus threatening water supply, and endanger coastal ecosystems and wetlands. Higher flood levels increase the risks to life and property, including sea dikes and other infrastructure, with possible follow-up effects on tourism, recreation and transportation functions.

Damage associated with sea-level rise would frequently result from extreme events, such as storm surges. Most concern is centred on positive surge events where the surge adds to the tidal level and increases the risk of coastal flooding by extreme water levels. Changes in the climatology of extreme water levels may result from changes in time mean local sea level (i.e. the local sea level relative to land averaged over a year), changes in tides, or changes in storm surge characteristics. Changes in storm surge characteristics are closely linked to changes in the characteristics of atmospheric storms, including the frequency, track and intensity of the storms. The height of surges is also strongly affected by regional and local-scale geographical features, such as the shape of the coastline. Typically, the highest water levels are found on the rising limb of the tide. The biggest surge events typically occur during the winter months inEurope.

The most obvious impact of extreme sea levels is flooding. The most well-known coastal flooding event in Europein living memory occurred in 1953 due to a combination of a severe storm surge and a high spring tide. The event caused in excess of 2 000 deaths in Belgium, the Netherlands and the UK, and damaged or destroyed more than 40 000 buildings. Currently around 200 million people live in the coastal zone in Europe, and insurable losses due to coastal flooding are likely to rise during the 21st century, at least for the North Sea region.

Indicator definition

This indicator comprises several metrics to describe past and future sea-level rise globally and in European seas. Global sea-level rise is reported because it is the second-most important metric of global climate change (after global mean surface temperature), and because it is a proxy of sea-level rise in Europe. Past sea-level trends across Europe are reported in two different ways: first, absolute sea level change based on satellite altimeter measurements that reflect primarily the contribution of global climate change to sea-level rise in Europe; second, relative sea-level change based on tide gauges that also include local land movement, which is more relevant for the development of regional adaptation strategies.

The following components on observed sea-level rise are included:

Change in global mean sea level (time series starting in 1880, in mm), based on a reconstruction from various data sources (since 1880) and on satellite altimeter data (since 1993)

Trend in absolute sea level across Europe (map, in mm/year), based on satellite measurements (since 1992)

Trend in relative sea level across Europe (map, in mm/year), based on selected European tide gauge stations (since 1970)

Furthermore, this indicator presents projections for sea level rise in the 21st century, both globally and for the European seas. The indidator also presents the contributions to past and future global sea level rise from different sources.

Finally, the indicator presents information on observed and projected changes in extreme sea level along European coasts. However, due to insufficient data availability this information cannot be presented by means of figures or maps.

Units

Sea level rise (mm)

Rate of sea level rise (mm/yr)

Policy context and targets

Context description

In April 2013 the European Commission presented the EU Adaptation Strategy Package (http://ec.europa.eu/clima/policies/adaptation/what/documentation_en.htm). This package consists of the EU Strategy on adaptation to climate change /* COM/2013/0216 final */ and a number of supporting documents. One of the objectives of the EU Adaptation Strategy is Better informed decision-making, which should occur through Bridging the knowledge gap and Further developing Climate-ADAPT as the ‘one-stop shop’ for adaptation information in Europe. Further objectives include Promoting action by Member States and Climate-proofing EU action: promoting adaptation in key vulnerable sectors. Many EU Member States have already taken action, such as by adopting national adaptation strategies, and several have also prepared action plans on climate change adaptation.

The European Commission and the European Environment Agency have developed the European Climate Adaptation Platform (Climate-ADAPT, http://climate-adapt.eea.europa.eu/) to share knowledge on observed and projected climate change and its impacts on environmental and social systems and on human health; on relevant research; on EU, national and subnational adaptation strategies and plans; and on adaptation case studies.

Adaptation means anticipating the adverse effects of climate change and taking appropriate action to prevent or minimise the damage they can cause, or taking advantage of opportunities that may arise. It has been shown that well planned, early adaptation action saves money and lives in the future. This web portal provides information on all adaptation activities of the European Commission.

In April 2013, the European Commission adopted an EU strategy on adaptation to climate change, which has been welcomed by the EU Member States. The strategy aims to make Europe more climate-resilient. By taking a coherent approach and providing for improved coordination, it enhances the preparedness and capacity of all governance levels to respond to the impacts of climate change.

Key policy question

What is the trend in mean sea level globally and across European seas?

Methodology

Methodology for indicator calculation

Sea-level changes are measured using tide gauges and remotely from space using altimeters.

Currently there are two main approaches to projecting future sea level: physically-based models that represent the most important known processes, and statistical models that apply the observed relationship between temperature or radiative forcing on the one hand and sea level on the other hand in the past and extrapolate it to the future. Both approaches produce a spread of results, which results in large uncertainties around future sea-level rise.

As far as the satellite altimetry derived indicator is concerned, the global sea level trends are calculated from the along-track T/P Jason-1&2 series of sea level anomalies obtained. For the regional mean sea level, other altimetry missions (Envisat, ERS-1, ERS-2, Geosat-FollowOn) are also used after being adjusted on these reference missions in order to compute mean sea level at high latitudes (higher than 66°N and S), and also to improve spatial resolution by combining all these missions together. The data are corrected for seasonal variations and the inverse barometer effects. There is a correction for post-glacial rebound. For the global trend maps defined on a 1/3° Mercator-grid the maps combining all available altimeter data are used. Data are provided by CSIRO (Australia). For the Mediterranean and Black Seas, regional products defined on a 1/8° grid are used. Data are provided by the MyOcean project.

Methodology for gap filling

Model-based projections for changes in regional sea level rise included only grid cells that are covered at least half by sea. Data for other grid cells partly covered by land and by sea were extrapolated using the nearest-neighbour method.

Data sources in latest figures

Uncertainties

Methodology uncertainty

See under "Methodology"

Data sets uncertainty

Changes in global average sea level result from a combination of several physical processes. Thermal expansion of the oceans occurs as a result of warming ocean water. Additional water is added to the ocean from a net melting of glaciers and small ice caps, and from the large Greenland and West Antarctic ice sheets. Further contributions may come from changes in the storage of liquid water on land, either in natural reservoirs such as groundwater or man-made reservoirs.

The locally experienced changes in sea level differ from global average changes for various reasons. Changes in water density are not expected to be spatially uniform, and changes in ocean circulation also have regionally different impacts. At any particular location there may also be a vertical movement of the land in either direction, for example due to the post-glacial rebound (in northern Europe) or to local groundwater extraction.

Projections from process-based models with likely ranges and median values for global-mean sea level rise and its contributions in 2081–2100 relative to 1986–2005 have been made for the four RCP scenarios and scenario SRES A1B used in the AR4. The contributions from ice sheets include the contributions from ice-sheet rapid dynamical change. The contributions from ice-sheet rapid dynamics and anthropogenic land water storage have been treated as having uniform probability distributions, and as independent of scenario (except that a higher rate of change is used for Greenland ice-sheet outflow under RCP8.5).